System.IO.LockFile.Internal

Low-level API for providing exclusive access to a resource using lock file.

Locking primitives

lock :: (MonadMask m, MonadIO m) => LockingParameters -> FilePath -> Throws LockingException m Handle

Open lock file write PID of a current process in to it and return its handle.

If operation doesn't succeed, then LockingException is raised. See also LockingParameters and RetryStrategy for details.

unlock :: (MonadMask m, MonadIO m) => FilePath -> Handle -> Throws LockingException m ()

Close lock file handle and then delete it.

Configuration

data LockingParameters

Locking algorithm parameters. When in doubt, use def, otherwise start with it. Example:

lockedDo
    :: (MonadMask m, MonadIO m)
    => FilePath
    -> m a
    -> Throws LockingException m a
lockedDo = withLockFile lockParams lockFile
  where
    lockParams = def
        { retryToAcquireLock = NumberOfTimes 3
        }

    lockFile = withLockExt "/var/lock/my-app"

Constructors

LockingParameters

Fields

retryToAcquireLock :: !RetryStrategy

Strategy for handling situations when lock-file is already acquired.

sleepBetweenRetires :: !Word64

Sleep interval in microseconds.

Instances

Eq LockingParameters

Data LockingParameters

Read LockingParameters

Show LockingParameters

Generic LockingParameters

Default LockingParameters

Defined as:

def = LockingParameters
    { retryToAcquireLock  = def
    , sleepBetweenRetires = 8000000  -- 8 seconds
    }

Sleep interval is inspired by lockfile command line utility that is part of Procmail.

Typeable * LockingParameters

type Rep LockingParameters

data RetryStrategy

Defines strategy for handling situations when lock-file is already acquired.

Constructors

No

Don't retry at all.

Indefinitely

Retry indefinitely.

NumberOfTimes !Word8

Retry only specified number of times. If equal to zero then it is interpreted same way as No.

Instances

Eq RetryStrategy

Data RetryStrategy

Read RetryStrategy

Show RetryStrategy

Generic RetryStrategy

Default RetryStrategy

Defined as: def = Indefinitely

Typeable * RetryStrategy

type Rep RetryStrategy

Exceptions

data LockingException

Constructors

UnableToAcquireLockFile FilePath

Wasn't able to aquire lock file specified as an argument.

CaughtIOException IOException

IOException occurred while creating or removing lock file.

Instances

Show LockingException

Exception LockingException

HiddenException LockingException

Typeable * LockingException